The focus of the research in this proposal is on the effects of alteration in dendritic cable properties on the conduction of the synaptic potential generated at dendritic sites and the distribution of the synaptic contacts on the dendrites. Two experimental approaches will be used to alter dendritic cable length. The first employs membrane ion channel blockers to increase specific membrane resistance and hence, increase the membrane time constant. This will have the effect of decreasing the effective dendritic cable length. This should be reflected in the cable parameters extracted from an analysis of voltage decays and the shape paprameters (rise-time and half-width) of the epsp generated at a dendritic site. The second method relies on the changes in dendritic tree structure following axotomy of the postsynaptic neuron. Our evidence suggests that there is a decrease in dendritic length and loss of many of the fine dendritic branches in corroboration of the work of Fishman (1975). When the length of the dendrites is plotted as a function of electrical distance we have shown that the space constant is shorter. During this period the cell electrical parameters including membrane time constant, soma to dendritic conductance ratio, and electrotonic length of the equivalent cylinder will be determined. We wish to determine what happens to the physiological and structural relationship during chromatolysis between an identified presynaptic axon whose synaptic distribution is known. This includes changes in synaptic potential shape and redistribution of synaptic contacts.